Add LOCAL_NOSANITIZE.

This can be used to selectively disable individual sanitizers on a
target. For example, some parts of libc should be built with
SafeStack (when requested with SANITIZE_TARGET), but never with
AddressSanitizer. Current build rules specify LOCAL_SANITIZE := never
to disable AddressSanitizer; the idea is to change that to
LOCAL_NOSANITIZE := address thread.

Bug: 27729263
Change-Id: I2b770f2ce3faf6ad6798792327e96adb86fe4a4f
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 9ca880b..7733a3e 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -189,6 +189,7 @@
 LOCAL_DPI_FILE_STEM:=
 LOCAL_SANITIZE:=
 LOCAL_SANITIZE_RECOVER:=
+LOCAL_NOSANITIZE:=
 LOCAL_DBUS_PROXY_PREFIX:=
 LOCAL_INIT_RC:=
 LOCAL_MODULE_HOST_OS:=